1. Field of the Invention
The present invention relates to an inferential system and inferential method which is used in an expert system and so forth.
2. Description of the Related Art
Recently, a computerized expert system which provides an intellectual function of human beings has been widely developed.
As an inferential method using such an expert system, a method named "Rete algorithm" is known.
This method uses a rule group comprising "if . . . then . . . " condition elements and execution elements, where a cycle of a pattern match, conflict resolution, and action (recognize-act cycle) is repeated and when there is no rule to pattern match, the inferential operation is completed.
In this method, current fact information is stored in a working memory. The pattern match operation is executed by comparing working memory elements stored in the working memory with LHS of rules.
The "if part" (condition elements) is called LHS (Left Hand Side) and the "then part" (execution elements) is called RHS (Right Hand Side).
However, there may be two or more combinations of the working memory elements and the rules which are matched. It is named a conflict set.
This conflict can be solved using conflict resolution strategies.
One of them uses time tags.
The time tags are numbers assigned to working memory elements. Each time tag represents the order of each working memory element created in the working memory.
For example with this method, it is possible to resolve the conflict in the strategy that "any rule which matches the most recent working memory element is executed with the highest priority".
The RHS of the rule which is selected by resolution the conflict is actually executed. Thus, the working memory elements in the working memory are modified, added, or deleted.
In addition, a time tag which represents the order of the creation is added to a working memory element which is newly created in the working memory.
In other words, the larger the value of the time tag, the more newly the working memory element has been created.
However, in the expert systems which have been implemented, when an inferential operation is continuously executed in real time, the values of the time tags increase until the last inferential result is obtained. Consequently, an overflow often occurs in the time tags.